Method of activating catalyst for carbon monoxide removal, catalyst for removing carbon monoxide, method of removing carbon monoxide, and method of operating fuel cell system

ABSTRACT

A carbon monoxide removing catalyst such as a ruthenium supporting catalyst is provided for removing, through oxidation thereof, carbon monoxide from an alcohol reformed gas containing hydrogen and carbon monoxide to be supplied to a fuel cell. For its activation, the catalyst is caused to contact an inactive gas or a hydrogen-containing inactive gas consisting of less than 50 volume % of hydrogen gas and the remaining volume of inactive gas, thereby to avoid poisoning of the electrode of the fuel cell with carbon monoxide.

TECHNICAL FIELD

[0001] The present invention relates to a carbon-monoxide removing(removal) catalyst for removing mainly carbon monoxide from a gascontaining hydrogen (H₂) gas as the major component thereof andcontaining also a small amount of carbon monoxide (CO) gas, such as areformed gas obtained by reforming (steam reforming, partial oxidationreforming, etc.) a hydrocarbon such as a natural gas, naphtha, keroseneor the like and an alcohol such as methanol. The invention relates alsoto a method of removing carbon monoxide therefrom.

BACKGROUND ART

[0002] Conventionally, with a fuel reforming apparatus for manufacturingreformed gas (gas containing 40 volume % or more (dry base) of hydrogen)with using fossil fuel such as natural gas as raw material, the rawmaterial was desulfurized and steam-reformed through a desulfurizer anda steam reformer disposed one after another, thereby to obtain thereformed gas containing hydrogen as the major component thereof andcarbon monoxide, carbon dioxide (CO₂), water (H₂O), etc. Further, with afuel reforming apparatus using an alcohol such as methane as the rawmaterial, the apparatus includes a methanol reformer incorporating amethanol reforming catalyst, thereby to obtain, from methanol, areformed gas containing hydrogen as the major component thereof andcarbon monoxide, carbon dioxide, water, etc.

[0003] Here, with a fuel reforming apparatus for making a reformed gasfor use in a phosphoric acid fuel cell, it is known that the electrodecatalyst of the fuel cell is poisoned by the presence of carbonmonoxide. Therefore, in order to prevent poisoning of the electrodecatalyst, the gas containing hydrogen as the major component thereof wasintroduced to a carbon-monoxide shift converter for converting carbonmonoxide into carbon dioxide (CO₂) through a carbon monoxide shiftconverting reaction, thereby to obtain a reformed gas with the carbonmonoxide concentration in the gas being lower than a predetermined value(e.g. 0.5%).

[0004] However, in the case of a fuel reforming apparatus for producinga reformed gas for use in a polymer electrolyte fuel cell, since thispolymer electrolyte fuel cell operates at a low temperature of about 80°C., its electrode catalyst will be poisoned even if just a trace amountof carbon monoxide is present. Therefore, it is necessary to furtherreduce carbon monoxide to be contained in the reformed gas. So, on thedownstream of the carbon monoxide shift converter, there was provided acarbon monoxide remover incorporating a carbon monoxide removingcatalyst for removing carbon monoxide. With this, the reformed gastreated by the carbon monoxide shift converter was introduced, withaddition thereto of an oxidizer such as air, to the carbon monoxideremover, so that carbon monoxide was oxidized into carbon dioxide in thepresence of this carbon monoxide removing catalyst, whereby a reformedgas with reduced carbon monoxide concentration lower than apredetermined concentration (e.g. 100 ppm or lower) was obtained.

[0005] As this type of carbon monoxide removing catalyst, there isemployed a precious metal catalyst comprising ruthenium (Ru), rhodium(Rh), platinum (Pt), palladium (Pd) or the like supported on a supportmade of e.g. alumina. And, conventionally, such catalyst was directlyput for use in the elimination of carbon monoxide, without effecting anyactivating treatment on the catalyst. Or, there was proposed anactivating method in which the carbon monoxide removing catalyst issubjected to a pre-treatment in a gas atmosphere containing hydrogen asthe major component thereof (50 mol % or more) and then the catalyst isput to use without being exposed to air (see Japanese Patent Application“Kokai ” No.: Hei. 10-29802). This may be because exposure to air isbelieved to lead to reduction in the catalyst activity.

[0006] However, in order to remove carbon monoxide from theabove-described reformed gas to achieve its concentration of 10 ppm orless by using the conventional carbon monoxide removing catalyst, it wasnecessary to add an excessive amount of oxidizer (oxygen) thereto.Moreover, when the carbon monoxide removing catalyst is to be used at alow temperature (e.g. near 100° C.), its catalyst activity is low, sothat carbon monoxide could not be removed effectively. Accordingly, inorder to remove a greater amount of carbon monoxide, it was necessary touse the carbon monoxide removing catalyst at a high temperature range(near about 200° C.) so as to enhance its activity.

[0007] When carbon monoxide is to be removed from the above-describedmixture gas containing hydrogen and carbon monoxide, it is known thatthe carbon monoxide removing catalyst employed would provide not onlythe useful effect of removing carbon monoxide, but also side reactionswhich consume the hydrogen contained in the mixture gas to producecarbon monoxide, methane, and water (respectively referred to as areverse shift reaction of carbon dioxide, a methanation reaction ofcarbon dioxide, and combustion reaction of hydrogen). Especially, theseside reactions are apt to occur when the temperature of the carbonmonoxide removing catalyst is high (e.g. 200° C. or higher).

[0008] Therefore, if the carbon monoxide removing catalyst is used at ahigh temperature range in order to remove a greater amount of carbonmonoxide, there occurs the problem of the above-described methanationreaction being very much promoted. This is problematic not only in thatthe hydrogen needed by the fuel cell is consumed inadvertently in themethanation reaction, but also in that the temperature will be furtherelevated due to the reaction heat from the methanation reaction.Moreover, there is still another problem of the carbon monoxide removingcatalyst being poisoned with iron, thus resulting in performancedegradation.

[0009] In this regard, the following mechanism is believed to beresponsible for the poisoning of the carbon monoxide removing catalystwith iron. First, when a high-temperature reaction gas containinghydrogen and carbon monoxide is introduced into the carbon monoxideremover, bonding occurs between the carbon monoxide and iron containedin the stainless steel forming a reaction tube of the carbon monoxideremover, thereby to produce a compound similar in structure to ironcarbonyl (Fe(CO)₅). As this iron carbonyl moves together with themixture gas to adhere to the catalyst portion of the carbon monoxideremover, this carbon monoxide removing catalyst will be poisoned. Onemethod to avoid this poisoning of the carbon monoxide removing catalystwith iron, there is known a method for rendering the temperature of thereaction gas to be introduced to be lower than 100° C. so as to preventproduction of the iron carbonyl inside the reaction tube. As describedabove, such method for protecting the carbon monoxide removing catalystagainst iron poisoning is also required.

[0010] Moreover, if a large amount of water is contained in the reactiongas to be introduced into the carbon monoxide remover, the water willaggregate and form dew within the pipe or carbon monoxide remover if thetemperature of the reaction gas introduced to an inlet of the carbonmonoxide remover is reduced to 100° C. or lower. The dew formation canresult in random variations in the cross sectional area and the volumeof the reaction gas passage within the carbon monoxide remover, whichresults, in turn, in random variation of the flow rate of the reactiongas being supplied into the carbon monoxide remover and/or in wetting ofthe carbon monoxide removing catalyst housed in the carbon monoxideremover with the aggregated water, leading to reduction in its activity.

[0011] The present invention has been made in view of theabove-described drawbacks and its object is to provide a method ofactivating a carbon monoxide removing catalyst for activating the carbonmonoxide removing catalyst for removing, mainly through its oxidation,carbon monoxide present in a mixture gas containing hydrogen and thecarbon monoxide by causing the catalyst to contact an inactive gas or ahydrogen-containing inactive gas consisting of less than 50 volume % ofhydrogen gas and the remaining volume of inactive gas.

DISCLOSURE OF THE INVENTION

[0012] For accomplishing the first object noted above, the inventionmethod of activating a carbon monoxide removing catalyst has firstthrough fifth characterizing features described below.

[0013] The first characterizing feature resides in that in the carbonmonoxide removing catalyst for removing, through oxidation thereof,carbon monoxide present in the mixture gas containing hydrogen and thecarbon monoxide is activated by being caused to contact an inactive gasor a hydrogen-containing inactive gas consisting of less than 50 volume% of hydrogen gas and the remaining volume of inactive gas.

[0014] Through extensive research, the present inventors discovered thatthe carbon monoxide removing catalyst can be significantly activated bybeing caused to contact an inactive gas or a hydrogen-containinginactive gas consisting of less than 50 volume % of hydrogen gas and theremaining volume of inactive gas and has perfected this invention basedon this discovery. When the carbon monoxide remover accommodatingtherein the carbon monoxide removing catalyst activated in the mannerdescribed above is operated at a low temperature (e.g. 70 to 120° C.), agood carbon monoxide removing activity can be obtained from the start ofthe operation. Incidentally, it has been revealed that if a low ratio ofhydrogen is added to the above-described inactive gas, the carbonmonoxide removing catalyst after the activation can provide highoxidation performance and also energy consumption can be restricted evenwhen the activating temperature for the carbon monoxide removingcatalyst is lowered. In practice, less than 50 volume % is sufficient asthe ratio of the hydrogen to be added to the inactive gas.

[0015] With the above, the carbon monoxide remover is capable ofreducing the carbon monoxide concentration in the reformed gas to belower than a predetermined value from the start of its operation; and ahigh-quality reformed gas which can be supplied even to a polymerelectrolyte fuel cell can be obtained with minimizing the loss ofhydrogen due to the side reactions. Further, it is also possible toremove the trouble of preparing in stock a large amount ofhigh-concentration hydrogen gas for the sole purpose of the activationof the carbon monoxide removing catalyst. Here, the term: nactive gasrefers to a gas which alone does not react with the carbon monoxideremoving catalyst.

[0016] The second characterizing feature resides in that said inactivegas contains at least one kind of gas selected from the group consistingof nitrogen gas, helium gas, argon gas and carbon dioxide gas.

[0017] With this, such gas selected from the group consisting ofnitrogen gas, helium gas, argon gas and carbon dioxide gas can beavailable at a relatively low cost and can be readily stored. Further,as such gas hardly reacts with materials forming other components thanthe carbon monoxide removing catalyst, the trouble of corrosion willhardly occur.

[0018] The third characterizing feature resides in that saidhydrogen-containing inactive gas consists of less than 10 volume % ofhydrogen gas and the remaining volume of the inactive gas.

[0019] With this feature, as will become apparent from the disclosure ofthe embodiment, even when the concentration of the hydrogen gas to beadded to the inactive gas is lower than 10 volume %, this will besufficient for enhancing the initial activity of the carbon monoxideremoving catalyst.

[0020] Further, the gas having such composition provides a uniqueadvantage of being usable also as a gas to be supplied for reduction ofthe catalyst in the carbon monoxide shift converter disposed upstream ofthe carbon monoxide remover or the catalyst in the alcohol reformer(e.g. the methanol reformer). That is to say, the catalysts to beincorporated within the alcohol reformer and the carbon monoxide shiftconverter can be easily oxidized. For this reason, copper-zinc typecatalyst is generally available in the form of copper oxide-zincmonoxide as an oxide. And, the catalyst as such oxide is charged into aeach receptacle and then heated under reducing gas (hydrogen gas)atmosphere for reducing the copper oxide into copper and then put touse.

[0021] In the above, with this type of catalyst, if the concentration ofhydrogen gas used in the reducing operation is high, the hydrogen gaswill violently react with the catalyst to generate heat, which wouldtend to result in sintering. Such sintering will deteriorate thecatalyst. For this reason, according to the convention, the hydrogen gaswas diluted to be lower than 10 volume % with the inactive gas such asnitrogen gas and supplied in this diluted form and then subjected to thereducing treatment at 260° C. or lower, thereby to restrict the heatgeneration. On the other hand, in the case of the carbon monoxideremoving catalyst (e.g. comprising alumina as its support and rutheniumsupported thereon), as ruthenium has high resistance against oxidation,it was believed that the catalyst can be used without effecting anyreducing treatment before use, if a reducing treatment is effected whenruthenium is supported on the alumina support.

[0022] Accordingly, it was not known that the carbon monoxide removingcatalyst can be activated by gas obtained by diluting the hydrogen gasto be lower than 10 volume % with an inactive gas such as nitrogen gas.And, the present inventors new finding resides in that the gas havingthe same composition as above can effect simultaneously and continuouslyboth the reduction of the alcohol reforming catalyst or the carbonmonoxide shift converting catalyst and the activation of the carbonmonoxide removing catalyst.

[0023] With the above, in providing any necessary facilities for theactivating process as a pre-treatment of the fuel reforming apparatusbefore its use, it becomes unnecessary to provide separately e.g. areducing facility and material for the carbon monoxide reformingcatalyst and a pre-treatment facility and material for the carbonmonoxide removing catalyst.

[0024] The fourth characterizing feature resides in that the activationof the carbon monoxide removing catalyst is effected at from 80° C. to400° C.

[0025] With this characterizing feature, if the activation is effectedat a temperature higher than 80° C., as shown in FIGS. 3-5 and Tables 1and 2, in e.g. production of the reforming gas, the concentration ofcarbon monoxide present in the mixture gas may be reduced significantly.Incidentally, if the activation is effected at a temperature higher than400° C., this will lead to not only disadvantageous increase in theenergy required for the heating, but also to risk of sintering of thecatalyst. Hence, the activation should be effected in the range from 80to 400° C.

[0026] More preferably, if the temperature of activation is from 120 to250° C., regardless of presence/absence of hydrogen in the inactive gas,it becomes possible to reduce the concentration of carbon monoxidepresent in the mixture gas to be lower than 100 ppm from the initialstage of the reaction (see FIGS. 3 through 5 and Tables 1 and 2).

[0027] Further, in the case of activation with the inactive gascontaining less than 10 volume % of hydrogen gas, by effecting thisactivation at from 80 to 250° C., the concentration of carbon monoxidepresent in the mixture can be reduced from 5000 ppm to less than 50 or100 ppm (see FIGS. 3 through 5 and Table 2). Further, if the activationis effected at from 120 to 250° C., the carbon monoxide concentrationcan be reduced to be lower than 10 ppm (see FIGS. 3 through 5 and Table2). If the carbon monoxide concentration is reduced to such level, thiswill provide an effect of significantly restricting the poisoning of theelectrode catalyst of the fuel cell with carbon monoxide, thereby toextend the service life of the electrode catalyst.

[0028] The fifth characterizing feature resides in that the mixture gascontaining hydrogen and carbon monoxide comprises a reformed gasobtained by reforming a hydrocarbon or an alcohol.

[0029] With this characterizing feature, when the mixture gas containinghydrogen and carbon monoxide comprises a reformed gas obtained byreforming a hydrocarbon or an alcohol, if the carbon monoxide removingcatalyst is activated by the method of activating carbon monoxideremoving catalyst according to any one of the above-described firstthrough fourth characterizing features, the carbon monoxide present inthe reformed gas may be removed to a low concentration, so that ahigh-quality reformed gas usable for a polymer electrolyte fuel cell canbe obtained advantageously.

[0030] The carbon monoxide removing catalyst also relating to thepresent invention has sixth through ninth characterizing featuresdescribed next.

[0031] The sixth characterizing feature resides in that a carbonmonoxide removing catalyst for removing carbon monoxide from a mixturegas containing hydrogen and the carbon monoxide, the catalyst beingformed by supporting ruthenium on a support, wherein 50% or more ofruthenium atoms present in a surface portion of the catalyst layer asdetermined by ESCA are present as ruthenium in the form of metal.

[0032] With this characterizing feature, 50% or more of the rutheniumatoms present on the surface of the carbon monoxide removing catalystare present as ruthenium in the form of metal (Ru(O)), the catalystfunction on the ruthenium catalyst surface is under an activatedcondition. As a result, it is possible to remove carbon monoxide over awider temperature range and to a lower concentration than theconventional carbon monoxide removing catalyst. Specifically, even whenthe carbon monoxide removing catalyst is used at a low temperature ofabout 100° C. to about 120° C. where the activity of the conventionalcatalyst is low, the carbon monoxide concentration can be reduced to alow level of 10 ppm or lower. As described above, since the carbonmonoxide removing catalyst can effectively remove carbon monoxide evenwhen used at a low temperature range, it is possible to restrictsufficiently the side reactions represented by the methanation of carbondioxide which was a problem in case of the convention when the catalystis employed at a high temperature and the carbon monoxide can be reducedselectively.

[0033] The seventh characterizing feature resides in that a carbonmonoxide removing catalyst for removing carbon monoxide from a mixturegas containing hydrogen and the carbon monoxide, the catalyst beingformed by supporting ruthenium on a support, wherein the carbon monoxideis activated by being caused to contact an inactive gas or ahydrogen-containing inactive gas consisting of less than 50 volume % ofhydrogen gas and the remaining volume of inactive gas so that 50% ormore of ruthenium atoms present on a surface layer of the catalyst asdetermined by ESCA are present as ruthenium in the form of metal.

[0034] With this characterizing feature, the catalyst is activated bybeing caused to contact an inactive gas or a hydrogen-containinginactive gas consisting of less than 50 volume % of hydrogen gas and theremaining volume of inactive gas so that 50% or more of ruthenium atomspresent in the surface portion of the catalyst layer as determined byESCA are present as ruthenium in the form of metal. So that, thecatalyst function on the ruthenium catalyst surface is under anactivated condition. As a result, it is possible to remove carbonmonoxide over a wider temperature range and to a lower concentrationthan the conventional carbon monoxide removing catalyst. Specifically,even when the carbon monoxide removing catalyst is used at a lowtemperature of about 100° C. where the activity of the conventionalcatalyst is low, the carbon monoxide concentration can be reduced to alow level of 10 ppm or lower. As described above, since the carbonmonoxide removing catalyst can effectively remove carbon monoxide evenwhen used at a low temperature range, it is possible to restrictsufficiently the side reactions represented by the methanation of carbondioxide which was a problem in case of the convention when the catalystis employed at a high temperature and the carbon monoxide can be reducedselectively.

[0035] The eighth characterizing feature resides in that 65% or more ofruthenium atoms present on a surface layer of the catalyst as determinedby ESCA are present as ruthenium in the form of metal.

[0036] With this characterizing feature, as 65% or more of rutheniumatoms present in the surface portion of the catalyst layer as determinedby ESCA are present as ruthenium in the form of metal (Ru(O)), thecatalyst function on the ruthenium catalyst surface is under an evenmore activated condition. As result, carbon monoxide can be removed evenmore effectively.

[0037] The ninth characterizing feature resides in that the supportcomprises alumina.

[0038] With this characterizing feature, if the support comprisesalumina, the material for the support is available inexpensively. Inaddition, thanks to its structural feature, there can be obtained afurther effect of increased effective area of the catalyst. As a result,as a greater amount of catalyst reaction can occur on the catalystsurface, carbon monoxide can be effectively removed.

[0039] The method of removing carbon monoxide also relating to thepresent invention has tenth through fourteenth characterizing featuresdescribed below.

[0040] The tenth characterizing feature resides in that a carbonmonoxide removing catalyst for removing, through oxidation thereof,carbon monoxide present in the mixture gas containing hydrogen andcarbon monoxide is caused to contact an inactive gas or ahydrogen-containing inactive gas consisting of less than 50 volume % ofhydrogen gas and the remaining volume of inactive gas to be activatedthereby and then the mixture gas and an oxidizer are allowed to react onthe carbon monoxide removing catalyst thereby to remove the carbonmonoxide.

[0041] With this characterizing feature, by activating a carbon monoxideremoving catalyst for removing, through oxidation thereof, carbonmonoxide present in the mixture gas containing hydrogen and carbonmonoxide by causing the catalyst to contact an inactive gas or ahydrogen-containing inactive gas consisting of less than 50 volume % ofhydrogen gas and the remaining volume of inactive gas and causing themixture gas and an oxidizer to react on the carbon monoxide removingcatalyst thereby to remove the carbon monoxide, the concentration of thecarbon monoxide present in the mixture gas may be reduced to be lowerthan a predetermined value. As a result, a high-quality reformed gaswhich can be supplied even to a polymer electrolyte fuel cell can beobtained with minimizing the loss of hydrogen due to the side reactions.Further, it is also possible to remove the trouble of preparing in stocka large amount of high-concentration hydrogen gas for the sole purposeof the activation of the carbon monoxide removing catalyst.

[0042] The eleventh characterizing feature resides in that saidhydrogen-containing inactive gas consists of less than 10 volume % ofhydrogen gas and the remaining volume of the inactive gas.

[0043] With this characterizing feature, said hydrogen-containinginactive gas consists of less than 10 volume % of hydrogen gas and theremaining volume of the inactive gas. Then, this gas is usable also as agas to be supplied for reduction of the catalyst in the carbon monoxideshift converter or the catalyst in the alcohol reformer (e.g. themethanol reformer) disposed upstream of the carbon monoxide remover.

[0044] Here, if the carbon monoxide removing catalyst is activated withthe hydrogen-containing inactive gas at from 80 to 250° C., theconcentration of carbon monoxide present in the mixture can be reducedto be less than 100 ppm (see FIGS. 3 through 5 and Table 2). Further, ifthe carbon monoxide concentration is reduced to such level, it ispossible to obtain the mixture gas which can be supplied to the solidpolymer fuel cell from the beginning of the operation of the carbonmonoxide remover. Further, if the activation is effected at atemperature from 120 to 250° C., it is possible to reduce the carbonmonoxide concentration to be lower than 10 ppm (see FIGS. 3 through 5and Table 2). If the carbon monoxide concentration is reduced to suchlevel, this will provide an effect of significantly restricting thepoisoning of the electrode catalyst of the fuel cell with carbonmonoxide, thereby to extend the service life of the electrode catalyst.

[0045] The twelfth characterizing feature resides in that the methodcomprises the steps of: introducing a reaction gas comprising saidmixture gas and an oxidizer added thereto into a carbon monoxide removerhaving a housing accommodating therein said carbon monoxide removingcatalyst according any one of the sixth through ninth characterizingfeatures and removing the carbon monoxide by causing said oxidizer andsaid mixture gas to react on said carbon monoxide removing catalyst.

[0046] With this characterizing feature, in the method comprising thesteps of: introducing a reaction gas comprising said mixture gas and anoxidizer added thereto into a carbon monoxide remover having a housingaccommodating therein said carbon monoxide removing catalyst andremoving the carbon monoxide by causing said oxidizer and said mixturegas to react on said carbon monoxide removing catalyst, 50% or more ofruthenium atoms present in the surface portion of the catalyst layer asdetermined by ESCA are present as ruthenium in the form of metal. Hence,the catalyst function on the ruthenium catalyst surface is under anactivated condition. As a result, it is possible to remove carbonmonoxide introduced into the carbon monoxide remover during theintroducing step. Specifically, even when the carbon monoxide removingcatalyst is used at a low temperature of about 100° C. where theactivity of the conventional catalyst is low, the carbon monoxideconcentration can be reduced to a low level of 10 ppm or lower. Asdescribed above, since the carbon monoxide removing catalyst caneffectively remove carbon monoxide even when used at a low temperaturerange, it is possible to restrict sufficiently the side reactionsrepresented by the methanation of carbon dioxide which was a problem incase of the convention when the catalyst is employed at a hightemperature and the carbon monoxide can be reduced selectively.

[0047] The thirteenth characterizing feature resides in that in theintroducing step, the reaction gas is introduced at a temperature lowerthan 100° C.

[0048] With this characterizing feature, in the method comprising thesteps of: introducing a reaction gas comprising said mixture gas and anoxidizer added thereto into a carbon monoxide remover having a housingaccommodating therein said carbon monoxide removing catalyst andremoving the carbon monoxide by causing said oxidizer and said mixturegas to react on said carbon monoxide removing catalyst, if in theintroducing step, the reaction gas is introduced at a temperature lowerthan 100° C., generation of iron carbonyl can be restricted, probablydue to bonding between iron constituting the pipe or the like and carbonmonoxide becomes difficult to occur. Further, even if the iron carbonylwere generated, since its boiling point is 103° C., evaporation thereofcan be restricted by maintaining the reaction gas at the temperaturelower than 100° C., whereby introduction of iron carbonyl into thecarbon monoxide remover disposed downstream of the pipe can beeffectively restricted. As a result, iron poisoning of the carbonmonoxide removing catalyst can be avoided.

[0049] The fourteenth characterizing feature resides in that thereaction gas has a dew point of 60° C. or lower.

[0050] With this characterizing feature, by adapting the reaction gasintroduced to the entrance of the carbon monoxide remover to have a dewpoint of 60° C. or lower under the processing pressure, even if alow-temperature reaction gas is introduced to the carbon monoxideremover in order to avoid iron poisoning, it is still possible toprevent dew formation of moisture present in the reaction gas inside thecarbon monoxide remover. Therefore, as this restricts wetting of thecarbon monoxide removing catalyst, degradation in the activity of thecatalyst function will hardly occur and also the amount of variation inthe flow amount of the reaction gas inside the pipe or inside the carbonmonoxide remover can be effectively minimized.

[0051] Further, a method of operating a fuel cell system also relatingto the present invention has fifteenth and sixteenth characterizingfeatures described below.

[0052] The fifteenth characterizing feature resides in that a method ofoperating a fuel cell system including in a supply passage for areformed gas to be supplied to a fuel cell from the upstream sidethereof: a carbon monoxide shift converter having a housingaccommodating therein a carbon monoxide shift converting catalyst forconverting carbon monoxide present in the reformed gas into carbondioxide and a carbon monoxide remover accommodating a carbon monoxideremoving catalyst for removing, through oxidation thereof, the carbonmonoxide present in the reformed gas, in the mentioned order, the methodcomprising the steps of: supplying a hydrogen-containing inactive gasconsisting of less than 10 volume % of hydrogen gas and the remainingvolume of inactive gas to said carbon monoxide shift converter and saidcarbon monoxide remover thereby to reduce said carbon monoxide shiftconverting catalyst and also to activate said carbon monoxide removingcatalyst and then initiating carbon monoxide shift reaction and carbonmonoxide removal reaction on said reformed gas.

[0053] With this characterizing feature, in operating a fuel cell systemincluding in a supply passage for a reformed gas to be supplied to afuel cell from the upstream side thereof: a carbon monoxide shiftconverter having a housing accommodating therein a carbon monoxide shiftconverting catalyst for converting carbon monoxide present in thereformed gas into carbon dioxide and a carbon monoxide removeraccommodating a carbon monoxide removing catalyst for removing, throughoxidation thereof, the carbon monoxide present in the reformed gas, inthe mentioned order, by supplying a hydrogen-containing inactive gasconsisting of less than 10 volume % of hydrogen gas and the remainingvolume of inactive gas to said carbon monoxide shift converter and saidcarbon monoxide remover thereby to reduce said carbon monoxide shiftconverting catalyst and also to activate said carbon monoxide removingcatalyst and then initiating carbon monoxide conversion and carbonmonoxide elimination on said reformed gas, the carbon monoxide removercan reduce the carbon monoxide concentration of the reformed gas to belower than a predetermined value from the start of its operation. Hence,a high-quality reformed gas which can be supplied even to a polymerelectrolyte fuel cell can be obtained with minimizing the loss ofhydrogen due to the side reactions. Further, as will become apparentfrom the disclosure of the embodiment, as the activating temperaturerequired for ensuring sufficient initial activity of the carbon monoxideremoving catalyst is reduced compared with the case of providing only aninactive gas not containing hydrogen, the energy consumption can berestricted.

[0054] Further, the gas having such composition provides a uniqueadvantage of being usable also as a gas to be supplied for reduction ofthe catalyst in the carbon monoxide shift converter disposed upstream ofthe carbon monoxide remover. Therefore, it is possible to effectsimultaneously and continuously both the reduction of the carbonmonoxide converting catalyst and the activation of the carbon monoxideshift removing catalyst. And, in providing any necessary facilities forthe activating process as a pre-treatment of the fuel reformingapparatus before its use, it becomes unnecessary to provide separatelye.g. a reducing facility and material for the carbon monoxide reformingcatalyst and a pre-treatment facility and material for the carbonmonoxide removing catalyst.

[0055] Here, if the carbon monoxide removing catalyst is activated withthe hydrogen-containing inactive gas at from 80 to 250° C., theconcentration of carbon monoxide present in the reformed gas can bereduced to be less than 100 ppm (see FIGS. 3 through 5 and Table 2).Further, if the carbon monoxide concentration is reduced to such level,it is possible to obtain the reformed gas which can be supplied to thesolid polymer fuel cell from the beginning of the operation of thecarbon monoxide remover. Further, if the activation is effected at atemperature from 120 to 250° C., it is possible to reduce the carbonmonoxide concentration to be lower than 10 ppm (see FIGS. 3 through 5and Table 2). If the carbon monoxide concentration is reduced to suchlevel, this will provide an effect of significantly restricting thepoisoning of the electrode catalyst of the fuel cell with carbonmonoxide, thereby to extend the service life of the electrode catalyst.

[0056] The sixteenth characterizing feature resides in that a method ofoperating a fuel cell system including in a supply passage for areformed gas to be supplied to a fuel cell from the upstream sidethereof: a methanol reformer accommodating a methanol reforming catalystfor reforming methanol and a carbon monoxide remover accommodating acarbon monoxide removing catalyst for removing, through oxidationthereof, the carbon monoxide present in the reformed gas, in thementioned order, the method comprising the steps of: supplying ahydrogen-containing inactive gas consisting of less than 10 volume % ofhydrogen gas and the remaining volume of inactive gas to said methanolreformer and said carbon monoxide remover thereby to reduce saidmethanol reforming catalyst and also to activate said carbon monoxideremoving catalyst and then initiating methanol reforming reaction andcarbon monoxide removal reaction on said reformed gas.

[0057] With this characterizing feature, in operating a fuel cell systemincluding in a supply passage for a reformed gas to be supplied to afuel cell from the upstream side thereof: a methanol reformeraccommodating a methanol reforming catalyst for reforming methanol and acarbon monoxide remover accommodating a carbon monoxide removingcatalyst for removing, through oxidation thereof, the carbon monoxidepresent in the reformed gas, in the mentioned order, by supplying ahydrogen-containing inactive gas consisting of less than 10 volume % ofhydrogen gas and the remaining volume of inactive gas to said methanolreformer and said carbon monoxide remover thereby to reduce saidmethanol reforming catalyst and also to activate said carbon monoxideremoving catalyst and then initiating methanol reforming and carbonmonoxide elimination on said reformed gas, the carbon monoxide removercan reduce the carbon monoxide concentration of the reformed gas to belower than a predetermined value from the start of its operation. Hence,a high-quality reformed gas which can be supplied even to a polymerelectrolyte fuel cell can be obtained with minimizing the loss ofhydrogen due to the side reactions. Further, as will become apparentfrom the disclosure of the embodiment, as the activating temperaturerequired for ensuring sufficient initial activity of the carbon monoxideremoving catalyst is reduced compared with the case of providing only aninactive gas not containing hydrogen, the energy consumption can berestricted.

[0058] Further, the gas having such composition provides a uniqueadvantage of being usable also as a gas to be supplied for reduction ofthe catalyst in the methanol reformer disposed upstream of the carbonmonoxide remover. Therefore, it is possible to effect simultaneously andcontinuously both the reduction of the methanol reforming catalyst andthe activation of the carbon monoxide removing catalyst. And, inproviding any necessary facilities for the activating process as apre-treatment of the fuel reforming apparatus before its use, it becomesunnecessary to provide separately e.g. a reducing facility and materialfor the methanol reforming catalyst and a pre-treatment facility andmaterial for the carbon monoxide removing catalyst.

[0059] Here, if the carbon monoxide removing catalyst is activated withthe hydrogen-containing inactive gas at from 80 to 250° C., theconcentration of carbon monoxide present in the reformed gas can bereduced to be less than 100 ppm (see FIGS. 3 through 5 and Table 2).Further, if the carbon monoxide concentration is reduced to such level,it is possible to obtain the reformed gas which can be supplied to thesolid polymer fuel cell from the beginning of the operation of thecarbon monoxide remover. Further, if the activation is effected at atemperature from 120 to 250° C., it is possible to reduce the carbonmonoxide concentration to be lower than 10 ppm (see FIGS. 3 through 5and Table 2). If the carbon monoxide concentration is reduced to suchlevel, this will provide an effect of significantly restricting thepoisoning of the electrode catalyst of the fuel cell with carbonmonoxide, thereby to extend the service life of the electrode catalyst.

BRIEF DESCRIPTION OF THE DRAWINGS

[0060]FIG. 1 is a conception diagram of a fuel cell system in which thepresent invention may be embodied,

[0061]FIG. 2 is a construction diagram of a carbon monoxide remover,

[0062]FIG. 3 is a graph showing effect of the embodiment of the presentinvention,

[0063]FIG. 4 is a graph showing effect of the embodiment of the presentinvention,

[0064]FIG. 5 is a graph showing effect of the embodiment of the presentinvention,

[0065]FIG. 6 is a graph illustrating relationship between a temperatureof a catalyst layer and a concentration of carbon monoxide for eachratio of presence of ruthenium (Catalyst A),

[0066]FIG. 7 is a graph showing relationship between a temperature of acatalyst layer and a concentration of carbon monoxide for each ratio ofpresence of ruthenium (Catalyst B),

[0067]FIG. 8 is a graph showing relationship between a temperature of acatalyst layer and a concentration of carbon monoxide for each ratio ofpresence of water steam,

[0068]FIG. 9 is a graph showing relationship between a temperature of acatalyst layer and a concentration of carbon monoxide, and

[0069]FIG. 10 is a graph showing relationship between a temperature of acatalyst layer and a concentration of carbon monoxide.

BEST MODE FOR EMBODYING THE INVENTION

[0070] In the following discussion, construction of a carbon monoxideremoving catalyst and a carbon monoxide removing method using thecatalyst both relating to the present invention will be described by wayof example of a polymer electrolyte fuel cell system for generatingelectric power by using a reformed gas.

[0071]FIG. 1 is a block diagram of a fuel reforming system whichoperates to produce from a raw fuel of natural gas (city gas) a reformedgas containing hydrogen as the major component thereof and then toremove carbon monoxide contained in the reformed gas and supply thisreformed gas to a fuel cell for electric power generation. Specifically,the system comprises a pipe (made of e.g. stainless steel)-connectedassembly of a raw fuel supplying line 1 receiving the natural gas as theraw fuel, a desulfurizer 2 accommodating a desulfurizing catalyst, adesulfurizing agent and so on, a reformer 4 accommodating a reformingcatalyst, a carbon monoxide shift converter 5 accommodating a carbonmonoxide shift converting catalyst, and a carbon monoxide remover 6accommodating a carbon monoxide removing catalyst (e.g. comprising asupport of alumina and ruthenium supported thereon). The reformed gasreformed by its passage through this fuel reforming system comprises agas containing hydrogen as its major component thereof. And, this gas issupplied to a polymer electrolyte fuel cell 7 for electric powergeneration. Incidentally, in the present application, the systemextending from the raw fuel supplying line 1 to the polymer electrolytefuel cell 7 is generically referred to as the uel cell system

[0072] Here, the raw fuel supplying line 1 is connected to a gascylinder or gas pipe for receiving a predetermined raw fuel. Further,the desulfurizer 2 removes sulfur content contained in the raw fuel. Thegas exiting the desulfurizer 2 is mixed with a water vapor supplied froma water vapor generator 3 and then transported to the reformer 4, inwhich the gas is caused to contact the reforming catalyst so that thehydrocarbons present in the raw fuel will be reformed mainly intohydrogen and also into carbon monoxide and carbon dioxide as byproducts.The reformed gas thus obtained is rich in hydrogen, but still containsabout ten and a few % of carbon monoxide as the byproduct. Therefore,the gas with this composition cannot be supplied directly to the polymerelectrolyte fuel cell 7. Then, at the carbon monoxide shift converter 5,the gas is caused to contact its carbon monoxide shift convertingcatalyst such as copper-zinc type catalyst, whereby the carbon monoxidepresent in the gas is converted into carbon dioxide and theconcentration of carbon monoxide is reduced to about 0.5 to 1%.

[0073] Further, this reformed gas whose carbon monoxide concentrationhas been reduced to 0.5 to 1% is mixed with air (its oxygen acts as anoxidizer) supplied from an oxidizing agent supplier 9 and this mixturegas is introduced as a reaction gas via the pipe into the carbonmonoxide remover 6. This carbon monoxide remover 6 is constructed suchthat a catalyst layer 12 comprising the carbon monoxide removingcatalyst is accommodated in its housing for allowing passage of thereaction gas through the catalyst layer 12.

[0074]FIG. 2 shows the construction of the carbon monoxide remover 6.

[0075] This carbon monoxide remover 6 includes the catalyst layer 12disposed inside a reaction tube 11 made of SUS and charged with thecarbon monoxide removing catalyst, a heater or a heat source for heatingthe SUS reaction tube 11 as the housing, and a temperature adjustingmeans 8 disposed along the outer periphery of the SUS reaction tube 11and having a cooling unit for cooling this SUS reaction tube 11. Thetemperature of the catalyst layer 12 is monitored by a temperaturemonitoring means 13 comprised of e.g. a thermocouple and as thetemperature adjusting means 8 operates based on its monitor result, thetemperature of the catalyst layer 12 is adjusted. Incidentally, as shownin FIG. 2, the temperature monitoring means 13 is disposed so as toextend through the catalyst layer 12 from its upstream side forreceiving the reaction gas to its downstream side, so that thetemperature of a desired portion from the upstream side to thedownstream side of the catalyst layer 12 can be determined by using thethermocouple. And, by determining the temperatures of the respectiveportions by moving the thermocouple from the upstream side to thedownstream side, the maximum temperature of the catalyst layer 12 can bedetermined. Further, a mechanism may be provided which is capable ofmonitoring and adjusting not only the temperature of the catalyst layer12 but also the temperature of the reaction tube 11. In this case, themonitoring means 13 may be disposed at the interface between thecatalyst layer 12 and the reaction tube 11. The temperature of thereaction tube 11 described below is the temperature of a portion of thisreaction tube 11 which portion corresponds to a mid portion (in themiddle between the upstream end and the downstream end) relative to thecatalyst layer 12.

[0076] For example, in order to restrict degradation of the activity dueto adherence of iron-containing compound such as iron carbonyl ormetalic iron entering the catalyst layer 12 to the carbon monoxideremoving catalyst surface and also to restrict the side reactions suchas methanation of carbon dioxide, the temperature adjusting means 8makes adjustment such that the maximum temperature of the catalyst layer12 may range between 130° C. and 180° C.

[0077] The reformed gas whose carbon monoxide concentration has beenreduced to 0.5 to 1% is caused to enter, together with the oxidizer, thehousing of the carbon monoxide remover 6, in which the gas is caused tocontact the catalyst layer 12 accommodated inside this housing. Thecatalyst layer 12 includes a carbon monoxide removing catalyst, suchthat mainly through the catalytic reaction of this carbon monoxideremoving catalyst, carbon monoxide reacts with oxygen to be oxidizedinto carbon dioxide. In this manner, the carbon monoxide present in thereformed gas is removed and consequently supplied to the polymerelectrolyte fuel cell 7 for electric power generation.

[0078] Further, along the outer wall face of some or all of the pipeinterconnecting the carbon monoxide shift converter 5 and the carbonmonoxide remover 6, there is disposed a heat exchanger 10, so that aheat transfer medium (such as air, water or the like) can flow withinthe heat exchanger via the wall surface of the pipe to beheat-exchangeable with the reformed gas or the reaction gas. Thedisposing position of this heat exchanger 10 may be before the positionwhere the oxidizer is added to the reformed gas as shown in FIG. 1 ormay also be at a position where the oxidizer has already been added tothe reformed gas and this is flowing as the reaction gas or even at aposition even more downstream. With occurrence of heat exchange betweenthe heat transfer medium flowing within the heat exchanger 10 and thereformed gas or reaction gas flowing within the pipe, the reformed gasor reaction gas will be cooled. Hence, by appropriately adjusting e.g.the flow rate of the heat transfer medium after determining in advancee.g. the flow rate, temperature of the reformed gas or reaction gas toenter the pipe, the temperature of the gas flowing from the portionwhere the heat exchanger 10 is disposed to the downstream side in thepipe is adjusted to be 100° C. or lower, preferably, lower than 80° C.,with consideration to e.g. possible load variation. Incidentally, thetemperature (lower limit) of the reaction gas will be determined, basedon such factors as the installing environment of the carbon monoxideremover 6, the temperature of the heat medium employed.

[0079] As described hereinbefore, by implementing at least either of theabove-described methods, i.e. the method of adjusting the temperature ofthe catalyst layer 12 to be higher than 130° C. and lower than 180° C.or the other method of adjusting the temperature of the pipe contactingthe upstream portion of the carbon monoxide remover 6 to a temperatureof 100° C. or lower, iron poisoning of the carbon monoxide removingcatalyst can be significantly restricted, thereby to improve the servicelife and the activity of the carbon monoxide removing catalyst. Further,if these methods are implemented together, with the resultant multipliereffect thereof, the service life and the activity of the carbon monoxideremoving catalyst may be even more improved.

[0080] Moreover, by providing a drain trap in the pipe to allowcondensation of the steam present in the reaction gas introduced intothe carbon monoxide remover 6 and setting the dew point of the reactiongas at 60° C. or lower, preferably 40° C. or lower under the processingpressure, then, it becomes possible to avoid dew formation within thepipe or the carbon monoxide remover.

[0081] Next, a method of preparing the carbon monoxide removing catalystwill be described.

[0082] First, a γ-alumina support in the form of a sphere of 2-4 mmdiameter was soaked in an aqueous solution of ruthenium trichloride toallow supporting of the ruthenium thereon by the impregnation method.After its drying, this was soaked in an aqueous solution of sodiumcarbonate and then washed with water and dried, whereby a precursor wasobtained. This precursor was soaked in hydrazine solution to reduce theruthenium present on the surface of the precursor and then water-washedagain. After this was dried at 105° C., a ruthenium/alumina catalyst wasobtained. It was observed that the supported ruthenium a was accumulatedin the thickness of a few tens of μm to a few hundreds of μm and insidethe catalyst most of the ruthenium atoms were present in the form ofmetal ruthenium, but in the vicinity of its surface, ruthenium compoundssuch as oxides, chlorides, hydroxides, or the like of ruthenium wereco-present with the metal ruthenium. Here, the supporting amount ofruthenium to be supported on the support is preferably 0.1 to 5 wt. %,more preferably 0.5 to 2 wt. %. Incidentally, although alumina wasemployed as the support in the present embodiment, other supports suchas of silica, titania, zeolite, etc. may also be employed.

[0083] 8 cc of the above-described ruthenium/alumina catalyst (carbonmonoxide removing catalyst) was charged into a stainless steel reactiontube (housing) 11 having an inner diameter of 21.2 mm and incorporatingtherein a thermocouple inserting sheath pipe having an outer diameter of6 mm, thereby to obtain the carbon monoxide remover 6. In operation, thegas introduced from the entrance of this carbon monoxide remover 6 willpass through the catalyst layer 12 and then be discharged from its exitto the outside of the housing.

[0084] Incidentally, with the catalysts to be employed in such fuel cellsystem, each catalyst is activated before the construction of theabove-described fuel cell system. Specifically, the catalystsincorporated respectively in the carbon monoxide shift converter 5 andthe carbon monoxide remover 6 will each be subjected to the treatmentrequired for its activation. Then, by shutting off introduction ofatmosphere and under this condition, each catalyst is connected with thepipe, thereby to be incorporated within the fuel cell system.

[0085] For instance, if the catalysts to be incorporated in the carbonmonoxide shift converter 5 and the carbon monoxide remover 6 are to bereduced and activated by different gases, then, the carbon monoxideshift converting catalyst incorporated in the carbon monoxide shiftconverter 5 will be reduced according to the standard method by beingheated to a temperature below 260° C. with introduction of the gas mixedwith 10 volume % or less of hydrogen gas. On the other hand, the carbonmonoxide removing catalyst incorporated in the carbon monoxide remover 6will be activated by the invention activating method, i.e. by using atleast one kind of inactive gas selected from the group consisting ofnitrogen gas, helium gas, argon gas and carbon dioxide gas or thehydrogen-containing inactive gas consisting of less than 50 volume % ofhydrogen gas and the remaining volume of inactive gas.

[0086] Preferably, the activating step is effected in the range of 80 to400° C. Further, in the case of the activation of the carbon monoxideremoving catalyst, the activating step is effected, preferably, in therange from 120 to 250° C. Moreover, in the case of the activation withthe hydrogen-containing inactive gas consisting of less than 10 volume %of hydrogen gas and the remaining volume of inactive gas, the activatingstep of the carbon monoxide removing catalyst is effected, preferably,at 80 to 250° C., more preferably, at 120 to 250° C.

[0087] Alternaively, according to this method, the gas used for thereduction of the carbon monoxide shift converting catalyst can be usedas it is for the activation of the carbon monoxide removing catalyst aswell.

[0088] Namely, under the condition of the carbon monoxide shiftconverter 5 and the carbon monoxide remover 6 being connected with eachother via the pipe, by maintaining the carbon monoxide shift converter 5and the carbon monoxide remover 6 under the temperature suitable for therespective reduction and activation thereof with introduction of thehydrogen-containing inactive gas consisting of less than 10 volume % ofhydrogen gas and the remaining volume of inactive gas., their reducingoperation and the activating operation both can be carried out. Withthis, the operations are possible with only one kind of activating(reducing) gas.

[0089] Incidentally, the reasons why the upper limit value for the ratio(volume %) of the hydrogen to be contained in the hydrogen-containinginactive gas for activating the carbon monoxide removing catalyst atless than 50 volume % are as follows. Firstly, if the carbon monoxideremoving catalyst is to be activated by using a gas containing hydrogenas the major component thereof, a large amount of hydrogen gas of a highconcentration will be required for the sole purpose of activation of thecarbon monoxide removing catalyst, hence being troublesome. Secondly,when this gas used in this activating process is discharged out of thesystem, there is the risk of the hydrogen concentration becoming theexplosion limit range (4 to 75 volume %) of hydrogen. Hence, anafter-treatment will be required.

[0090] Next, for the case of effecting the above-described activatingtreatment (pre-treatment) and the further case of not effecting thetreatment, results of determinations on the carbon monoxide removingabilities of those carbon monoxide removers 6 based on variations in thecarbon monoxide concentrations at the entrance and the exit of thesecarbon monoxide removers 6 will be discussed next. For the determinationof the carbon monoxide removing abilities, a simulated reaction gascontaining hydrogen, carbon monoxide and others was supplied to eachcarbon monoxide remover 6 and the outlet gas (exit gas) was sampled overtime at the exit of the carbon monoxide remover 6 and the concentrationof the carbon monoxide in this exit gas was determined by using a gaschromatograph apparatus including a thermal conductivity detector (TCD)and a hydrogen flame ionization detector (FID). Incidentally, thedetectable lower limit for carbon monoxide of this gas chromatographapparatus was 5 ppm in Examples 1-4 and Comparison Examples 1-3 and 1ppm in the other Examples and other embodiments.

EXAMPLE 1

[0091] As described hereinbefore, a carbon monoxide remover 6 wasprepared by charging, into a stainless steel reaction tube 11, 8 cc ofRu/alumina catalyst (carbon monoxide removing catalyst) including asupport of an alumina sphere of a diameter of 2 to 4 mm and ruthenium(Ru) supported on this support. This carbon monoxide remover 6 include atemperature adjusting means 8 having a heater capable of heating thereaction tube 11 from the outside and a cooler capable of cooling thetube, so that the temperature of the reaction tube 11 is controllable.

[0092] Then, while introducing the hydrogen-containing inactive gas(hydrogen: 6%, nitrogen: 94%) for activating the carbon monoxideremoving catalyst at the flow rate of 1000 cc/min. to this carbonmonoxide remover 6 (the ruthenium supporting amount of the carbonmonoxide removing catalyst: 1.0 wt. %), the remover was heated by thetemperature adjusting means until the reaction tube temperature reached250° C. and was maintained at 250° C. for 1.5 hours (pre-treatment).

[0093] After this pre-treatment, the temperature of the reaction tube 11was lowered to 100° C. and maintained at 100° C., and the simulatedreaction gas was introduced into the reaction tube 11 at space velocity(GHSV): 7500/h, thereby to allow an oxidation removal for carbonmonoxide to take place. Incidentally, the simulated reaction gasemployed was a gas having a composition (i.e. carbon monoxide: 0.5%,methane: 0.5%, carbon dioxide: 20.9%, oxygen: 0.8%, nitrogen: 3.1%,water (vapor): 5% and balanced with hydrogen) corresponding to theoutlet gas from the carbon monoxide shift converter 5 mixed with air toobtain an oxygen/carbon monoxide molar ratio of 1.6. FIG. 3 shows theexit (outlet) carbon monoxide concentration (determined by the gaschromatograph apparatus) obtained when the oxidation removal waseffected in the above-described manner.

EXAMPLE 2

[0094] While introducing the hydrogen-containing inactive gas (hydrogen:10 volume %, nitrogen: 90 volume %) for activating the carbon monoxideremoving catalyst at the flow rate of 1000 cc/min. to the carbonmonoxide remover 6 (1.0 wt. % for the ruthenium supporting amount of thecarbon monoxide removing catalyst), the remover was heated by thetemperature adjusting means until the reaction tube temperature reached200° C. and was maintained at 200° C. for 2 hours (pre-treatment).

[0095] After this pre-treatment, the temperature of the reaction tube 11was lowered to 110° C. and maintained at 110° C., and the simulatedreaction gas was introduced into the reaction tube 11 at space velocity(GHSV): 7500/h, thereby to allow an oxidizing removing reaction forcarbon monoxide to take place. Incidentally, the simulated reaction gasemployed was a gas having a composition (i.e. carbon monoxide: 0.5%,methane: 0.5%, carbon dioxide: 20.9%, oxygen: 0.8%, nitrogen: 3.1%,water (vapor): 20% and balanced with hydrogen) corresponding to the exit(outlet) gas from the carbon monoxide shift converter 5 mixed with airto obtain an oxygen/carbon monoxide molar ratio of 1.6. FIG. 4 shows theexit (outlet) carbon monoxide concentration (determined by the gaschromatograph apparatus) obtained when the oxidation removal waseffected in the above-described manner.

EXAMPLE 3

[0096] In this Example 3, by using the carbon monoxide remover 6 (0.5wt. % for the ruthenium supporting amount of the carbon monoxideremoving catalyst), the pre-treatment was effected in the same manner asExample 2, except for setting the oxidation removal temperature forcarbon monoxide to 120° C. FIG. 5 shows the exit (outlet) carbonmonoxide concentration (determined by the gas chromatograph apparatus)obtained when the oxidation removal was effected in the above-describedmanner.

Comparison Examples 1-3

[0097] Except for absence of the pre-treatment on the carbon monoxideremover 6, as Comparison Examples 1-3, experiments were conducted in thesame manner as Examples 1-3 above by effecting the oxidation removaldeterminations for carbon monoxide with using the simulated reactiongas.

[0098]FIGS. 3 through 5 respective show the exit (outlet) carbonmonoxide concentrations (determined by the gas chromatograph apparatus)obtained with the oxidation removal described above.

[0099] As shown in FIG. 3, with the carbon monoxide remover 6 using thecarbon monoxide removing catalyst activated by the invention method, theexit (outlet) carbon monoxide concentration (Example 1) was below thedetection limit (5 ppm) and upon start of the operation, there wasobtained a reformed gas which can be supplied as a fuel gas to thepolymer electrolyte fuel cell, demonstrating the distinguished effectfrom the activation of the carbon monoxide removing catalyst. On theother hand, in the cases of the absence of the pre-treatment (ComparisonExample 1), the exit (outlet) carbon monoxide concentration was 4758 ppmafter two hours from the start of operation and still was 4347 ppm after100 hours, demonstrating that a reformed gas which can be supplied asthe fuel gas to the polymer electrolyte fuel cell was not obtained, oreven the catalytic reaction hardly proceeded.

[0100] Further, as shown in FIGS. 4 and 5, in Examples 2 and 3 also, theexit (outlet) carbon monoxide concentrations were below the detectionlimit (5 ppm) and even under low temperature conditions of 100 to 120°C., there was obtained a reformed gas which can be supplied as the fuelgas to the polymer electrolyte fuel cell. On the other hand, in the caseof the conventional method (Comparison Examples 2 and 3) not effectingthe pre-treatment, the catalytic activity was hardly achieved at theinitial stage of operation and under a low temperature operationcondition, carbon monoxide of about 4000 ppm was contained in the exitgas.

EXAMPLE 4

[0101] The gaseous species and the treatment temperature to be used inthe pre-treatment were studied.

[0102] A carbon monoxide removing catalyst (ruthenium supporting amount:1.0 wt. %) charged in the carbon monoxide remover 6 was maintained at 80to 250° C. under the presence of the flow of nitrogen gas as an inactivegas which does not react with the carbon monoxide removing catalyst ornitrogen gas containing 10 volume % of hydrogen (hydrogen-containinginactive gas) and treated under these conditions for 2 hours.

[0103] To these, a gas having a composition corresponding to acomposition of the exit (outlet) gas from the carbon monoxide shiftconverter 5 added with air (carbon monoxide: 0.5%, methane: 0.5%, carbondioxide: 20.9%, oxygen: 0.85%, nitrogen: 3.4%, water (vapor): 20%, andbalanced with hydrogen) was introduced at the space velocity (GHSV):7500/hr. so as to achieve the oxygen/carbon monoxide molar ratio of 1.7.And, with maintaining the reaction tube temperature at 110° C., theoxidation removal for the carbon monoxide was allowed to occur, when theexit (outlet) carbon monoxide concentrations (determined by the gaschromatograph device) were determined. The results are shown in Table 1and Table 2. Incidentally, in Table 2, any concentration below thedetection limit (5 ppm) of the carbon monoxide concentration are allindicated as 5 ppm. TABLE 1 pre-treated with N₂ gas pre-treatment temp.(° C.) 120 250 exit CO concentration (ppm) 2 hrs  39  33 after start ofreaction exit CO concentration (ppm) 12 hrs  8  9 after start ofreaction

[0104] TABLE 2 pre-treated with 90 volume % N₂/10 volume % H₂ gaspre-treatment temp. (° C.) 80 120 200 250 exit CO concentration (ppm) 2hrs 40  5  5  5 after start of reaction exit CO concentration (ppm) 12hrs 10  5  5  5 after start of reaction

[0105] The carbon monoxide concentrations of fuel gas which can bedirectly supplied to a polymer electrolyte fuel cell are from 50 to 100ppm. Then, the effects of the activating treatments were evaluatedwhether the concentration reached this level or not. As a result, asshown in Table 1 above, with the activation with nitrogen gas alone, thecarbon monoxide could be reduced to the above-described level at 120 to250° C. Whereas, in the case of the activation with the nitrogen gascontaining 10 volume % of hydrogen, as shown in Table 2, the carbonmonoxide could be reduced to the above-described level at 80 to 250° C.Especially, when the activation was effected at a temperature higherthan 120° C., the carbon monoxide concentration could be reduced tobelow 5 ppm immediately after the start of the carbon monoxide removalreaction. If a reformed gas refined in this manner is supplied a polymerelectrolyte fuel cell, the poisoning of the electrode catalyst can berestricted effectively in particular.

[0106] It was found that by effecting the activation under suchconditions, from the timing immediately after start of operation of thecarbon monoxide remover 6, even in a relatively low temperature rangeand even with a small amount of oxidizing agent to be added, there stillcan be obtained a reformed gas which can be supplied directly to thepolymer electrolyte fuel cell so that the production efficiency of thereformed gas can be improved advantageously.

[0107] In the above, the nitrogen gas containing 10 volume % or less ofhydrogen can be used also as a reducing gas typically used foractivating (reducing) other catalyst, e.g. the carbon monoxide shiftconverting catalyst, to be used in the fuel reforming apparatus in whichthe carbon monoxide remover 6 is to be provided. Therefore, the reducinggas for e.g. the carbon monoxide shift converting catalyst describedabove can be used also as the gas to be used for the activation of thecarbon monoxide removing catalyst.

[0108] Next, changes on the surface of the catalyst layer which haveoccurred as the result of the activating treatment on the carbonmonoxide removing catalyst will be studied.

[0109] The catalysts employed in this experiment were three kinds ofCatalysts A through C (all of which were catalysts prior to thepre-treatment) shown in Table 3 below which were manufactured by theabove-described method of preparing making a carbon monoxide removingcatalyst, with these catalysts differing in the ratio of rutheniumpresent in the form of metal (Ru (O)) relative to all forms of theruthenium Incidentally, the three kinds of Catalysts A through C shownin Table 3 are not to be used directly for the carbon monoxide removalprocess. Rather, like the case described hereinbefore, they are to beused for the carbon monoxide removal process after undergoing apre-treatment to be detailed later. Therefore, the values of the ratiosof ruthenium in the form of metal shown in Table 3 are values obtainedprior to the pre-treatment. TABLE 3 ratio of Ru BET CO metal supportingsurface adsorption pore (Ru amount area amount diameter (O)) support (%)(m²/g) (cc/g) (mm) (%) Catalyst γ- 0.98 171 0.62 7.4 19.4 A aluminaCatalyst γ- 0.47 170 0.33 7.7 21.0 B alumina Catalyst γ- 0.98 166 1.27.1 11.8 C alumina

[0110] Incidentally, in this example, the average pore diameters weredetermined by the mercury penetration method with using: Autopore II9220 manufactured by Micromeritics Inc. (Shimadzu Co., Ltd.) Indetermination, the contact angle between mercury and the measurementsample was set at 130 degrees and the mercury penetrating pressure wasvaried from 3.447×10³ Pa (0.5 psi) to 4.137×10⁸ Pa (60,000 psi). Then,from total pore volume (V) and total pore specific surface area (S) inthe range of pore diameter of the carbon monoxide removing catalystobtained from the above, the average pore diameters (4V/S) were derived.Further, the adsorption amount of carbon monoxide was determined byusing a full automatic catalyst gas adsorption amount measuringapparatus (MODEL R6015) manufactured by Ohkura Riken Co., Ltd. and theBET surface area was measured by using a full automatic powder specificsurface area measuring apparatus (AMS8000) manufactured by Ohkura RikenCo., Ltd.

[0111] Before using the carbon monoxide remover 6 made in theabove-described manner for removing carbon monoxide, as a pre-treatmenttherefor, activating treatment on the carbon monoxide removing catalystcontained within the carbon monoxide remover 6 will be effected by usingthe inactive gas. By effecting this pre-treatment (activatingtreatment), the ratio of the metal (O valency) on the surface of themetal acting as a catalyst and supported on the support will increase,so that it may be expected that the catalytic effect will be greater.Next, the results of the experiment will be described with respect tothe ratio of the metal (O valency) when the pre-treatment was effectedand the resultant carbon monoxide removing effect.

[0112] In this example, the ratio of ruthenium present in the form ofmetal (0 valency) relative to the ruthenium atoms present in the surfaceof the catalyst was determined by ESCA (Electron Spectroscopy forChemical Analysis). This ESCA is referred to also as X-ray photoelectronspectroscopy (XPS). This method can identify not only the elementscontained in a sample, but also the bonding conditions among theseelements from the resultant photoelectron spectrum. Further, of thosephotoelectrons generated by the irradiation of X ray on the sample,those photoelectrons which can escape from the sample to the outside arephotoelectrons which were generated at a position shallower than apredetermined depth. Hence, the determined elements are only thoseelements present on the surface layer of the sample. In this example, onthe γ-alumina as the support, ruthenium is supported in the thickness ofabout a few tens of μm to a few hundreds of μm of the sample. The ESCAmethod determines only to the limited depth of a few tens of μm.Therefore, the surface layer portion determined by the ESCA can beconsidered as ruthenium which mainly acts as the catalyst. Incidentally,the ratio between ruthenium atoms present under the 0 valency condition(condition of metal) determined by the ESCA method and ruthenium atomspresent under the other conditions (in the conditions of oxide,chloride, hydroxide, etc.) was obtained through spectrum separation,thereby to obtain the ratio of the ruthenium present in the form ofmetal.

[0113] In this example, the ESCA determination was made by using PHI5700ESCA System manufactured by PHI Ltd. (Physical ElectronicsIndustries, Inc.). The determination conditions are as shown in Table 4and Table 5 below. TABLE 4 X ray parameters Source Standard anodematerial Mg (magnesium) anode energy 1253.6 eV anode power 400 W anodevoltage 14 kV work function 3.9 eV

[0114] TABLE 5 detector parameters detector multi-channel input lensomni-focus lens area minimum measuring range 800 μmφ

[0115] For activating the above-described carbon monoxide removingcatalysts: Catalysts A through C, while introducing thehydrogen-containing inactive gas (hydrogen: 9.5 volume %, nitrogen: 90.5volume %) at the flow rate of 1000 cc/min. into the carbon monoxideremovers 6 including these catalysts, the temperature of the reactiontube was adjusted to 100° C., 180° C. or 220° C. and then maintained atthese respective temperatures for 1.5 hours by the temperature adjustingmeans 8. Thereafter, while introducing nitrogen gas into the carbonmonoxide removers 6, the temperature of the respective catalyst layer 12was lowered to 70° C., thereby to prevent ruthenium present in the formof metal on the surface layer of the catalyst layer 12 from beingaffected by e.g. oxidizing effect. Then, the carbon monoxide removalperformance was determined. Incidentally, in the above case, thehydrogen-containing inactive gas used in the pre-treatment contains 10volume % or less of hydrogen (9.5 volume %) like the foregoing case, itis also possible to carry out substantially same pre-treatment withusing an inactive gas not containing hydrogen or otherhydrogen-containing inactive gas consisting of not more than 50 volume %of hydrogen gas and the remaining ratio of inactive gas, if apredetermined treatment temperature and/or period is appropriatelyselected. For instance, if the treatment temperature is raised or if theratio of hydrogen contained in the hydrogen-containing inactive gas isincreased, the treatment period may be shorter. Alternatively, if thetreatment temperature is lowered or if the ratio of hydrogen containedin the hydrogen-containing inactive gas is decreased, the treatmentperiod may be extended.

EXAMPLE 5

[0116] In this Example 5, Catalyst A was charged into the reaction tube11 to form the catalyst layer 12. Then, the pre-treatment was carriedout under the conditions shown in Table 6 below or the pre-treatment wasnot carried out, thereby to obtain carbon monoxide removers 6 (A1through A5) having different ratios of ruthenium present in the form ofmetal in the surface portion of the ruthenium catalyst. On these, thecarbon monoxide removing characteristics were studied. Incidentally, forA3 which did not undergo the pre-treatment with the hydrogen-containinginactive gas (hydrogen: 9.5 volume %, nitrogen: 90.5 volume %), thetemperature of the catalyst was raised to 70° C. while introducinghydrogen gas (1000 cc/min.) thereto and the catalyst was maintainedunder this condition for 1 hour with continued introduction of thehydrogen gas, thereby to allow the carbon monoxide removing reaction totake place. Similarly, for A4, the temperature was raised to 70° C.while introducing simulation gas (carbon monoxide; 0.5 volume %,methane: 0.5 volume %, carbon dioxide: 21 volume %, and hydrogen for therest) simulating the gas from the exit of the carbon monoxide shiftconverter 5 (1000 cc/min.), thereafter, the carbon monoxide removingreaction was allowed to occur. Also, for A5, the temperature of thecatalyst was raised to 70° C. while introducing nitrogen gas (1000cc/min.) and then the carbon monoxide removing reaction was allowed tooccur.

[0117] Incidentally, for each of the carbon monoxide removers (A1through A5) made in the above-described manner, the ratio of Ru(ruthenium) present in the form of metal in the surface portion of thecatalyst layer of the carbon monoxide removing catalyst prior to thecarbon monoxide removing reaction thereof was determined by the ESCA.The results are shown in Table 6 below.

[0118] Incidentally, in the graphs of the figures, the discretedetermined values are interconnected with a simple approximating curve,the curve segments between the adjacent determined values does notnecessarily reflect the present invention with accuracy. For instance,in the graph of A2 shown in FIG. 6, the temperature of the catalystlayer 12 sharply varies in the vicinity of about 120° C. However, if adetermination were effected with greater fineness between thetemperatures of 100° C. and 120° C. of the catalyst layer 12, it mightbe possible that the temperature sharply varies in the vicinity of about100° C. Therefore, it is reasonable to assume that in such temperaturerange involving sharp change in the determined value, an error may bepresent to a degree corresponding to the distance between adjacentdetermined temperatures (about 10° C. to about 20° C.) for the criticaltemperature when the carbon monoxide concentration at the exit of thecarbon monoxide remover 6 is below 10 ppm. TABLE 6 catalyst A1 A2 A3 A4A5 pre-treatment YES YES NO NO NO pre-treatment 180° C. 100° C. temp.pre-treatment 1.5 hrs. 1.5 hrs. period ratio of metal 68.6% 51.2% 31.2%28.2% 25.1% (Ru (O))

[0119]FIG. 6 shows the results of carbon monoxide removal reactions withthe carbon monoxide removers 6: A1 through A5 with introduction of asimulated reaction gas. From this FIG. 6, it can be seen that thegreater the ratio of ruthenium in the form of metal (Ru (O)), thegreater the carbon monoxide removing effect. In this, the vertical axisof the graph represents the carbon monoxide concentration (ppm) at theexit of the carbon monoxide remover 6, while the horizontal axisrepresents the maximum temperature (° C.) of the catalyst layer 12. Asshown, in the case of the greater ratios of ruthenium in the form ofmetal (A1, A2), the carbon monoxide can be reduced to 10 ppm or lower inthe temperature range of the catalyst layer 12 between about 100° C. toabout 180° C. (especially, from about 120° C. to about 180° C.) whichrange is believed to be desirable in terms of the activity of thecatalyst as well as restriction of the side reaction. On the other hand,in the case of the lower ratios of ruthenium in the form of metal (A3through A5), although the carbon monoxide concentration can be reducedto a sufficiently low value of 10 ppm when the maximum temperature ofthe catalyst layer 12 is higher than about 170° C. However, when thetemperature exceeds about 180° C., this will promote the methanationreaction as will be described later. Hence, these catalysts will not beuseful.

[0120] Here, the “simulated reaction gas ” refers to a gas simulating agas obtained by adding air as an oxidizer to the outlet gas of thecarbon monoxide shift converter 5, having a composition of: carbonmonoxide: 0.5%, methane: 0.5%, carbon dioxide: 21%, oxygen: 0.75%,nitrogen: 3.0%, and hydrogen for the rest. Such simulated reaction gaswas introduced into each carbon monoxide remover 6 at the space velocity(GHSV) of 7500/hr. The composition including its carbon monoxideconcentration of the simulated reaction gas is fixed for all examples.Hence, by comparing the carbon monoxide concentrations at the exit, thecarbon monoxide removal performances of the respective catalysts can beevaluated. Incidentally, in this example, the simulated reaction gas wasintroduced into each carbon monoxide remover 6 at the space velocity(GHSV) of 7500/hr. However, the space velocity may vary within the rangeof 500 to 50000/hr. More preferably, the space velocity is from 1000 to30000/hr.

[0121] The amount of oxygen contained in the air used as the oxidizingagent will be adjusted such that the molar ratio (O₂/CO) between carbonmonoxide and this oxygen in the simulated reaction gas may be preferably3 or less, more preferably less than 2 and most preferably 1.5 or less.

[0122] Further, as a typical example, the results of the experiments onthe carbon monoxide removing catalysts A1 and A4 are shown in Table 7and Table 8, respectively. As described hereinbefore, from Table 7 andTable 8, it is understood that the methanation reaction is promoted withthe increase in the temperature of the catalyst layer 12 and that thereis sudden occurrence of the methanation reaction of the carbon dioxidewhen the maximum temperature of the catalyst layer 12 exceeds about 180°C. With such methanation of carbon dioxide, this will result indisadvantageous consumption of the hydrogen in the simulated reactiongas. Furthermore, as the chain-reaction like progress of methanation ofcarbon dioxide, there will occur another problem of further increase inthe temperature of the catalyst layer 12 due to the reaction heat.Incidentally, in Table 7, concentrations lower than the detection lowerlimit (1 ppm) for carbon monoxide are all denoted as 0 ppm. TABLE 7 COremover 6 (Catalyst A1) reaction 70 80 100 120 140 160 170 tube temp. (°C.) CO 15.7 2.9 0 1.6 3.8 7 12.2 concentration (ppm) max temp. of 89 99120 141 163 186 200 catalyst layer (° C.) O₂ 86 0 0 0 0 0 0Concentration (ppm) CH₄ 5007 5057 5232 5790 7508 12659 18423concentration (ppm)

[0123] TABLE 8 CO remover 6 (Catalyst A4) reaction 70 80 100 120 140 160170 tub. temp. (° C.) CO 5012 4938 4506 41.8 10.4 8.6 12.4 concentration(ppm) Max temp. of 72 83 107 145 165 190 201 catalyst layer (° C.) O₂7276 7078 6241 84 0 0 0 Concentration (ppm) CH₄ 4965 4967 4967 5153 651713985 17065 concentration (ppm)

[0124] Accordingly, based on the confirmation that the methanationreaction of carbon dioxide is promoted when the maximum temperature ofthe catalyst layer 12 exceeds about 180° C., even if the carbon monoxideconcentration at the exit of the carbon monoxide remover 6 can bereduced to be e.g. 10 ppm or lower, it is inappropriate to employ thecarbon monoxide remover 6 at such temperature range.

EXAMPLE 6

[0125] In this Example 6, Catalyst B was charged into the reaction tube11 to form the catalyst layer 12. Then, the pretreatment was carried outunder the conditions shown in Table 7 below or the pre-treatment was notcarried out, thereby to obtain carbon monoxide removers 6 (B1 throughB3) having different ratios of ruthenium present in the form of metal(Ru (O)) in the surface portion of the ruthenium catalyst layer. Onthese, the carbon monoxide removing characteristics were studied.Incidentally, for B3 which did not undergo the pre-treatment with thehydrogen-containing inactive gas (hydrogen: 9.5 volume %, nitrogen: 90.5volume %), the temperature of the catalyst was raised to 70° C. whileintroducing simulation gas (carbon monoxide; 0.5volume %, methane: 0.5volume %, carbon dioxide: 21 volume %, and hydrogen for the rest)simulating the gas from the outlet of the carbon monoxide shiftconverter 5 (1000 cc/min.). Then, the carbon monoxide removalperformance was determined.

[0126] Incidentally, for each of the carbon monoxide removers 6 (B1through B3) made in the above-described manner, the ratio of Ru(ruthenium) present in the form of metal (Ru (O)) in the surface layerof the carbon monoxide removing catalyst prior to the carbon monoxideremoval reaction thereof was determined by the ESCA. The results areshown in Table 9 below. TABLE 9 catalyst B1 B2 B3 pre-treatment YES YESNO pre-treatment temp. 220° C. 180° C. pre-treatment period 1.5 hrs. 1.5hrs. ratio of metal Ru 72.4% 70.2% 26.9%

[0127]FIG. 7 shows the results of carbon monoxide removal reactionseffected by the carbon monoxide removers 6: B1 through B3 withintroduction of the simulated reaction gas. As shown in FIG. 7, like thecase of FIG. 6, it can be seen that the greater the ratio of rutheniumin the form of metal (Ru (O)), the greater the carbon monoxide removingeffect. As shown, in the case of the greater ratios of ruthenium in theform of metal (B1, B2), the carbon monoxide can be reduced to 10 ppm orlower in the temperature range of the catalyst layer 12 (temperaturerange of the maximum temperature of the catalyst layer 12) rage betweenabout 100° C. to about 180° C. (especially, from about 110° C. to about180° C.) which range is believed to be desirable in terms of theactivity of the catalyst as well as restriction of side reaction. On theother hand, in the case of the lower ratio of ruthenium in the form ofmetal (B3), although the carbon monoxide concentration can be reduced toa sufficiently low value of 10 ppm when the maximum temperature of thecatalyst layer 12 is higher than about 160° C. However, when thetemperature exceeds about 180° C., this will promote the methanationreaction as described above. Hence, this catalyst will not be useful.

EXAMPLE 7

[0128] In this Example 7, Catalyst C was charged into the reaction tube11 to form the catalyst layer 12. Then, the pre-treatment was carriedout under the conditions shown in Table 7 below or the pre-treatment wasnot carried out, thereby to obtain carbon monoxide removers 6 (C1through C3) having different ratios of ruthenium present in the form ofmetal (Ru (O)) in the surface layer of the ruthenium catalyst. On these,the carbon monoxide removing characteristics were studied. Incidentally,for C3 which did not undergo the pre-treatment with thehydrogen-containing inactive gas (hydrogen: 9.5 volume %, nitrogen: 90.5volume %), the temperature was raised to 70° C. while introducingsimulation gas (carbon monoxide; 0.5 volume %, methane: 0.5 volume %,carbon dioxide: 21 volume %, and hydrogen for the rest) simulating thegas from the outlet of the carbon monoxide shift converter 5 (1000cc/min.). Then, the carbon monoxide removal performance was determined.

[0129] Incidentally, for each of the carbon monoxide removers 6 (C1through C3) made in the above-described manner, the ratio of Ru(ruthenium) present in the form of metal in the surface layer of thecarbon monoxide removing catalyst prior to the carbon monoxide removalreaction thereof was determined by the ESCA. The results are shown inTable 10 below. TABLE 10 catalyst C1 C2 C3 pre-treatment YES YES NOpre-treatment temp. 220° C. 180° C. pre-treatment period 1.5 hrs. 1.5hrs. ratio of metal Ru 74.7% 63.4% 14.6%

[0130] Table 11 through Table 13 show the results of carbon monoxideremoval reactions effected by the carbon monoxide removers 6: C1 throughC3 with introduction of the simulated reaction gas. Incidentally, inTable 11, the concentrations lower than the detection lower limit (1ppm) for carbon monoxide are all shown as 0 ppm. As shown in Table 11through Table 13, like the case of FIG. 6 and FIG. 7, it can be seenthat the greater the ratio of ruthenium in the form of metal (Ru (O)),the greater the carbon monoxide removing effect. As shown, in the caseof the greater ratios of ruthenium in the form of metal (C1, C2), thecarbon monoxide removal reaction can take place sufficiently under suchlow temperature range of from about 70° C. to about 100° C. On the otherhand, in the case of the lower ratio of ruthenium in the form of metal(C3), the carbon monoxide removal reaction hardly occurs in thetemperature range from about 70° C. to about 100° C. TABLE 11 carbonmonoxide remover 6 (Catalyst C1) reaction tube temp. (° C.) 70  80 100CO concentration (ppm)  0  0  0 max temp. of catalyst layer (° C.) 93103 124

[0131] TABLE 12 carbon monoxide remover 6 (Catalyst C2) reaction tubetemp. (° C.) 70 80 100 CO concentration (ppm) 2.9 1.1 3.1 max temp. ofcatalyst layer (° C.) 90 100 121

[0132] TABLE 13 carbon monoxide remover 6 (Catalyst C3) reaction tubetemp. (° C.)  70  80  100 CO concentration (ppm) 4867 4837 2346 maxtemp. of catalyst layer (° C.)  72  84  114

[0133] As may be understood from Examples 5 though 7 described above, byeffecting the pre-treatment for increasing the ratio of rutheniumpresent in the form of metal (Ru (O)) on the catalyst layer, there isachieved the carbon monoxide remover 6 which can effectively reduce thecarbon monoxide concentration without the disadvantageous side reactionssuch as the methanation reaction of carbon dioxide. For obtaining suchcarbon monoxide remover 6, the pre-treatment was carried out by causingthe hydrogen-containing inactive gas containing 9.5 volume % of hydrogenand the inactive gas to contact the catalyst layer 12. Incidentally, inthese examples, the ratio of hydrogen contained in thehydrogen-containing inactive gas employed in the pre-treatment was setas 9.5 volume %. However, with a pre-treatment using otherhydrogen-containing inactive gas containing less than 50 volume % ofhydrogen and inactive gas, the above-described effect of thepre-treatment can be achieved as well.

[0134] In the above, the carbon monoxide removal performances weredetermined on the samples having different ratios of ruthenium presentin the form of metal (Ru (O)) in the surface portion of the catalystlayer. Then, as long as the ratio of ruthenium in the form of metalexceeds about 50% as shown in FIG. 6 and FIG. 7 as well as Tables 6through 13, it is possible to reduce the concentration of carbonmonoxide at the exit of the carbon monoxide remover 6 to a value as lowas about 10 ppm or less in the range of maximum temperature of thecatalyst layer 12 of from about 100 to about 180. Further, if the ratioof the ruthenium in the form of metal exceeds about 65%, as may beunderstood from the measurement result on Sample Al for instance, aneven greater carbon monoxide removing effect will appear. Furthermore,if the ratio of the ruthenium in the form of metal exceeds about 70%, asmay be understood from the measurement result on Sample C1 for instance,a still greater carbon monoxide removing effect will appear.Incidentally, as shown in Table 6, Table 9 and Table 10, this ratio ofruthenium in the form of metal can be increased by raising thepre-treatment temperature. In this respect, it should be noted, however,that an excessively high pre-treatment temperature is not desirablesince this may result in sintering of the catalyst. Also, the ratio ofruthenium present in the form of metal on the catalyst surface can beincreased also by extending the period of the pre-treatment.

[0135] In order to increase the ratio of ruthenium present in the formof metal (Ru (O)) in the surface portion of the catalyst layer, it ispreferred that the activation (pre-treatment) of the carbon monoxideremoving catalyst with the inactive gas or with the hydrogen-containinginactive gas containing less than 50 volume % be carried out in thetemperature range of from about 80° C. to about 400° C. Then, asdescribed above, more preferred temperature range as the pre-treatmenttemperature has been found out. Specifically, as shown in Tables 6through 13 and FIGS. 6 and 7, it was possible to increase the ratio ofruthenium present in the form of metal (Ru (O)) in the surface portionof the catalyst layer by the pretreatment effected at the temperatureshigher than 100° C. (e.g. about 100° C. to about 220° C.). In thisregard, as described above, the treatment temperature can be variedthrough adjustment of the amount of hydrogen contained in thehydrogen-containing inactive gas or the treatment period. Accordingly,for the purpose of increasing the ratio of ruthenium present in the formof metal in the surface portion of the catalyst layer, the pre-treatmentmay be effected at 250° C. or even at 400° C. In such case, thetreatment period and/or the amount of hydrogen contained in thehydrogen-containing inactive gas can be reduced. Conversely, in the caseof a lower treatment temperature of about 80° C., the above-describedpre-treatment is made possible by extending the treatment period and/orincreasing the amount of hydrogen contained in the hydrogen-containinginactive gas.

[0136] <Other Embodiments>

[0137] <1>

[0138] In Examples 5 through 7 described above, the gas not containingwater vapor was used as the simulated reaction gas. However, even whenthe simulated reaction gas contains water vapor, similar carbon monoxideremoving effect can be achieved. This will be explained next. For makingthe carbon monoxide remover 6, the Catalyst A described hereinbefore wascharged into the reaction tube 11 to form the catalyst layer 12. Then,on this, the pre-treatment was effected at 200° C. for 1 hour with usinga hydrogen-containing inactive gas having composition of: hydrogen: 5volume %, nitrogen: 95%, so that of the ruthenium present in the surfaceportion of the catalyst layer 12, 69% thereof was present in the form ofmetal. This was used in this example. The simulated reaction gasemployed here had the composition of: carbon monoxide: 0.5%, methane:0.5%, carbon dioxide: 21%, oxygen: 0.75%, nitrogen: 3.0% and hydrogenfor the rest. Then, to 1000 Nml/min of this mixture gas, water vapor wasadded by 20 volume %, 5 volume % or by 0 volume %. The other measurementconditions were the same as the foregoing examples. Incidentally, thereaction simulation gas was introduced to achieve GHSV value of 7500/hron the dry basis.

[0139] As may be understood from the result of measurement of carbonmonoxide concentration at the exit of the carbon monoxide remover 6shown in FIG. 8, the presence of water vapor in the simulated reactiongas does not affect the carbon monoxide removing performance and thecarbon monoxide concentration at the exit of the carbon monoxide remover6 can be reduced to such low value as less than 10 ppm.

[0140] <2>

[0141] In Examples 5 through 7 described above, after effecting thepre-treatment on the carbon monoxide removing catalyst, the gas presentinside the carbon monoxide remover 6 was replaced by nitrogen gas so asto prevent the catalyst layer from being oxidized. In this example,however, after the pre-treatment, the catalyst layer 12 was exposed toair. And, through determination of the carbon monoxide removingperformance of the carbon monoxide remover 6 using this catalyst layer12, it will be demonstrated next that even when the catalyst layer 12 isexposed to air, its performance as the carbon monoxide removing catalystwill hardly be affected and the catalyst can substantially maintain itscarbon monoxide removing effect as long as the ratio of rutheniumpresent in the form of metal is greater than 50%.

[0142] (Catalyst A′)

[0143] For obtaining this Catalyst A′ while the hydrogen-containinginactive gas (hydrogen: 9.5%, nitrogen: 90.5%) was introduced at therate of 1000 cc/min. to the Catalyst A under the conditions shown inTable 3, the temperature of the reaction tube was raised to 220° C. andmaintained at this temperature for 1.5 hours by the temperatureadjusting means 8, thereby to effect the pre-treatment on the catalyst.Thereafter, while its inside was being replaced by nitrogen gas (flowrate: 1000 cc/min.), the temperature of the catalyst layer 12 of thecarbon monoxide remover 6 was lowered to the room temperature and thenthe nitrogen replacement was stopped. Then, the catalyst layer 12 wasexposed to air at the room temperature for 30 hours, whereby theCatalyst A′ was obtained. The ratio of ruthenium present in the form ofmetal in the surface portion of the catalyst layer after its airexposure for 30 hours was 68.3%. Thereafter, like the foregoingexamples, while introducing nitrogen gas (1000 cc/min.), the temperaturewas raised to 70° C. Then, the concentration of carbon monoxide at theexit of the carbon monoxide remover 6 was determined. The othermeasurement conditions were the same as Examples 5 through 7 describedabove. The results of determination are shown in FIG. 9. Next, theeffect of exposing the catalyst layer 12 will be studied.

[0144]FIG. 9 shows that the catalyst layer 12 maintains its effect forreducing the carbon monoxide concentration to the level lower than 10ppm in the practical temperature range of about 100° C. to about 180° C.Therefore, it may be said that even when the catalyst layer 12 isexposed to air, its carbon monoxide removing performance will not besignificantly deteriorated as long as the ratio of ruthenium present inthe form of metal (Ru (O)) in the surface portion of the catalyst layeris maintained above 50%.

[0145] (Catalyst A″)

[0146] In the case of this Catalyst A ″, on the Catalyst A having theconditions shown in Table 3, the activating treatment was effected byraising the temperature of the reaction tube to 180° C. and maintainedat this temperature for 1.5 hours by the temperature adjusting means 8while introducing the hydrogen-containing inactive gas (hydrogen: 9.5%,nitrogen: 90.5%) at the rate of 1000 cc/min. Then, this was used firstfor carbon monoxide elimination. In this, the determination of thecarbon monoxide concentration at the exit of the carbon monoxide remover6 was effected when the maximum temperature of the catalyst layer 12 was123° C. (determination prior to air exposure). Thereafter, while itsinside was being replaced by nitrogen gas (flow rate: 1000 cc/min.), thetemperature of the catalyst layer 12 of the carbon monoxide remover 6was lowered to the room temperature and then the nitrogen replacementwas stopped. Then, the catalyst layer 12 was exposed to air at the roomtemperature for 24 hours. The ratio of ruthenium present in the form ofmetal in the surface portion of the catalyst layer after its airexposure for 24 hours was 59.5%. Thereafter, like the foregoingexamples, while introducing nitrogen gas (1000 cc/min.), the temperaturewas raised to 70° C. Then, the concentration of carbon monoxide at theexit of the carbon monoxide remover 6 was determined (measurement afterair exposure). The other measurement conditions were the foregoingexamples. The results of determination are shown in FIG. 10. Next, theeffect of the above will be studied.

[0147]FIG. 10 shows the carbon monoxide removing performance prior tothe air exposure and the carbon monoxide removing performance after theair exposure. It is shown that in either case, the catalyst maintainsits effect for reducing the carbon monoxide concentration to the levellower than 10 ppm in the practical temperature range of about 100° C. toabout 180° C. Therefore, it may be said that even when the catalystlayer 12 is exposed to air, its carbon monoxide removing performancewill not be significantly deteriorated as long as the ratio of rutheniumpresent in the form of metal (Ru (O)) in the surface portion of thecatalyst layer is maintained above 50%.

[0148] <3>

[0149] Next, there will be described results of experiment conducted tostudy whether deterioration with lapse of time would occur in the carbonmonoxide removing catalyst treated with the above-describedpre-treatment (activating treatment).

[0150] By effecting the pre-treatment with nitrogen gas containing 5volume % of hydrogen (hydrogen-containing inactive gas) on the CatalystA, there was obtained a catalyst layer 12 in which of the rutheniumatoms present in the surface portion of the catalyst layer, more than70% thereof was present in the form of metal (Ru (O)). Then, into acarbon monoxide remover 6 having this catalyst layer 12, the simulatedreaction gas was introduced to allow the carbon monoxide removingreaction to occur. Thereafter, determination was made again by the ESCAon the ratio of ruthenium present in the form of metal in the surfaceportion of the catalyst layer 12. This revealed that the ratio wasmaintained over 70%. Based on this, it may be said that the condition ofruthenium on the catalyst surface can be maintained after the catalysteffected the carbon monoxide removing reaction.

[0151] Separately from the above, by effecting the pre-treatment withnitrogen gas containing 5 volume % of hydrogen (hydrogen-containinginactive gas) on the Catalyst A, there was obtained a catalyst layer 12in which of the ruthenium atoms present in the surface portion of thecatalyst layer, more than 70% thereof was present in the form of metal(Ru (O)). Then, into a carbon monoxide remover 6 having this catalystlayer 12, the simulated reaction gas containing 5 volume % of watervapor (corresponding to the dew point of 33° C.) was introduced. And,with raising the temperature of the reaction tube 11 to 140° C., thedurability of the Catalyst A was investigated. Incidentally, in thisexperiment, the maximum temperature of the catalyst layer 12 was 160° C.The investigation revealed that the concentration of carbon monoxide atthe exit of the carbon monoxide remover 6 was maintained below 5 ppm forthe period of 4000 hours. In this way, it has been shown that the carbonmonoxide removing catalyst according to the present invention can stablyprovide its carbon monoxide removing effect for an extended period oftime.

[0152] <4>

[0153] Next, there will be described results of an experiment conductedto see whether improvement could be achieved in the performance of acarbon monoxide removing catalyst without the pre-treatment unlike thecase described above.

[0154] The catalyst layer 12 was prepared from the Catalyst B withoutthe pre-treatment. Then, into the carbon monoxide remover 6 includingthis catalyst layer 12 heated up to 70° C. in nitrogen gas, thesimulated reaction gas containing water vapor at the water vaporconcentration of 3 volume % (corresponding to a dew forming point of 25°C.) was introduced. Then, with setting the temperature of the reactiontube 11 to 80° C., the carbon monoxide removing reaction was allowed tooccur. In this condition, the carbon monoxide concentration at the exitof the carbon monoxide remover 6 immediately after the start of thereaction was determined to be 4600 ppm and the carbon monoxideconcentration at the exit of the carbon monoxide remover 6 wasdetermined to be still 4600 ppm even after lapse of 12 hours.Incidentally, after lapse of 12 hours, the catalyst layer 12 was takenout and its catalyst surface was analyzed by the ESCA. The analysisrevealed that of the ruthenium atoms in the surface portion of thecatalyst layer, 11.4% of them were ruthenium present in the form ofmetal (Ru (O)). As described above, the carbon monoxide removingperformance of the catalyst without the pre-treatment is low. And, evenwhen this catalyst was used for providing the carbon monoxide removingreaction, there was observed no improvement in its carbon monoxideremoving performance.

[0155] <5>

[0156] In the foregoing embodiment, the ratio of the ruthenium presentin the form of metal (Ru (O)) in the surface of the catalyst layer wasdetermined by using the ESCA. However, other analysis method may beused, provided such other method too provides substantially samemeasurement depth for the surface layer of the ruthenium catalyst.

[0157] <6>

[0158] With the carbon monoxide remover 6 made according to the presentinvention, the apparatus or device to be disposed upstream thereof isnot particularly limited. Therefore, the types of the desulfurizingcatalyst, reforming catalyst, carbon monoxide shift converting catalystemployed in the fuel gas reforming system are not limited in particular,but any conventional types of catalyst can be employed.

[0159] Further, the method of the invention can be used not only for theabove-described case of reforming the natural gas (methane), but alsofor elimination of carbon monoxide contained in a reformed gas obtainedthrough methanol reforming. In this, if the hydrogen-containing inactivegas consisting of 10 volume % or less of hydrogen and an inactive gas asthe remaining gas is used for such activation, this gas can be used alsoas a reducing gas typically employed for activation (reduction) of othercatalyst used in the fuel reforming system in which the carbon monoxideremover 6 is to be provided, e.g. an alcohol (methanol) reformingcatalyst used for reforming alcohol (methanol). Therefore, the reducinggas for the carbon monoxide shift converting catalyst or the alcoholreforming catalyst described above can be used also as an activating gasfor the carbon monoxide removing catalyst.

[0160] Incidentally, in the foregoing, nitrogen was employed as theinactive gas. Other gases such as helium gas, argon gas, or carbondioxide gas will be relatively inexpensively available and can be storedeasily. With use of such other gases too, since they hardly react withthe materials forming the other components than the carbon monoxideremoving catalyst, there will be achieved such effect as restrictingoccurrence of corrosion.

[0161] Industrial Applicability

[0162] With the method of activating carbon monoxide catalyst, thecarbon monoxide removing catalyst and the method of removing carbonmonoxide all proposed by the present invention, carbon monoxide can beeffectively removed even when the carbon monoxide removing catalyst isused at a low temperature range. Hence, it is possible to selectivelyreduce the carbon monoxide concentration without inviting the sidereactions represented by methanation of carbon dioxide which would beproblematic in the prior art using the catalyst at a high temperature.

[0163] Accordingly, in the case of a fuel cell system using the reformedgas obtained by the above-described apparatus construction, from thestart of its operation, the carbon monoxide concentration of thereformed gas supplied thereto has been reduced to be lower than apredetermined value. Thus, the reformed gas can be obtained withminimizing loss of hydrogen due to such side reactions. Further, sincethe carbon monoxide concentration of the supplied reformed gas can bevery low, the poisoning of the electrode catalyst in the fuel cell canbe restricted very effectively, so that the service life of theelectrode catalyst may be extended.

[0164] As described above, a reformed gas with a significantly reducedcarbon monoxide concentration can be obtained. Consequently, it becomespossible to generate electric power with higher efficiency than theconvention and to achieve the service life of the electric powergenerating system.

1. A method of activating a carbon monoxide removing catalyst forremoving, through oxidation thereof, carbon monoxide present in amixture gas containing hydrogen and the carbon monoxide, wherein thecatalyst is activated by being caused to contact an inactive gas or ahydrogen-containing inactive gas consisting of less than 50 volume % ofhydrogen gas and the remaining volume of inactive gas.
 2. The method ofactivating a carbon monoxide removing catalyst according to claim 1,wherein said inactive gas contains at least one kind of gas selectedfrom the group consisting of nitrogen gas, helium gas, argon gas andcarbon dioxide gas.
 3. The method of activating a carbon monoxideremoving catalyst according to claim 1, wherein said hydrogen-containinginactive gas consists of less than 10 volume % of hydrogen gas and theremaining volume of the inactive gas.
 4. The method of activating acarbon monoxide removing catalyst according to claim 1, wherein theactivation of the carbon monoxide removing catalyst is effected at from80° C. to 400° C.
 5. The method of activating a carbon monoxide removingcatalyst according to claim 1, wherein the mixture gas containinghydrogen and carbon monoxide comprises a reformed gas obtained byreforming a hydrocarbon or an alcohol.
 6. A carbon monoxide removingcatalyst for removing carbon monoxide from a mixture gas containinghydrogen and the carbon monoxide, the catalyst being formed bysupporting ruthenium on a support, wherein 50% or more of rutheniumatoms present in the surface portion of the catalyst layer as determinedby ESCA are present as ruthenium in the form of metal.
 7. A carbonmonoxide removing catalyst for removing carbon monoxide from a mixturegas containing hydrogen and the carbon monoxide, the catalyst beingformed by supporting ruthenium on a support, wherein the catalyst iscaused to contact an inactive gas or a hydrogen-containing inactive gasconsisting of less than 50 volume % of hydrogen gas and the remainingvolume of inactive gas so that 50% or more of ruthenium atoms present ona surface layer of the catalyst as determined by ESCA are present asruthenium in the form of metal.
 8. The carbon monoxide removing catalystaccording to claim 6 or 7, wherein 65% or more of ruthenium atomspresent on a surface layer of the catalyst as determined by ESCA arepresent as ruthenium in the form of metal.
 9. The carbon monoxideremoving catalyst according to claim 6 or 7, wherein the supportcomprises alumina.
 10. A method of removing carbon monoxide, wherein acarbon monoxide removing catalyst for removing, through oxidationthereof, carbon monoxide present in mixture gas containing hydrogen andthe catalyst is caused to contact an inactive gas or ahydrogen-containing inactive gas consisting of less than 50 volume % ofhydrogen gas and the remaining volume of inactive gas and causing themixture gas to be activated thereby and then the mixture gas and anoxidizer are allowed to react on the carbon monoxide removing catalystthereby to remove the carbon monoxide.
 11. The method of removing carbonmonoxide according to claim 10, wherein said hydrogen-containinginactive gas consists of less than 10 volume % of hydrogen gas and theremaining volume of the inactive gas.
 12. A method of removing carbonmonoxide comprising the steps of: introducing a reaction gas comprisingsaid mixture gas and an oxidizer added thereto into a carbon monoxideremover having a housing accommodating therein said carbon monoxideremoving catalyst according claim 6 or claim 7; and removing the carbonmonoxide by causing said oxidizer and said mixture gas to react on saidcarbon monoxide removing catalyst.
 13. The method of removing carbonmonoxide according to claim 12, wherein in the introducing step, thereaction gas is introduced at a temperature lower than 100° C.
 14. Themethod of removing carbon monoxide according to claim 12, wherein thereaction gas has a dew point of 60° C. or lower.
 15. A method ofoperating a fuel cell system including in a supply passage for areformed gas to be supplied to a fuel cell from the upstream sidethereof: a carbon monoxide shift converter accommodating therein acarbon monoxide shift converting catalyst for converting carbon monoxidepresent in the reformed gas into carbon dioxide and a carbon monoxideremover accommodating therein a carbon monoxide removing catalyst forremoving, through oxidation thereof, the carbon monoxide present in thereformed gas, in the mentioned order, the method comprising the stepsof: supplying a hydrogen-containing inactive gas consisting of less than10 volume % of hydrogen gas and the remaining volume of inactive gas tosaid carbon monoxide shift converter and said carbon monoxide removerthereby to reduce said carbon monoxide shift converting catalyst andalso to activate said carbon monoxide removing catalyst; and theninitiating carbon monoxide shift reaction and carbon monoxide removalreaction on said reformed gas.
 16. A method of operating a fuel cellsystem including in a supply passage for a reformed gas to be suppliedto a fuel cell from the upstream side thereof: a methanol reformertherein a methanol reforming catalyst for reforming methanol and acarbon monoxide remover accommodating a carbon monoxide removingcatalyst for removing, through oxidation thereof, the carbon monoxidepresent in the reformed gas, in the mentioned order, the methodcomprising the steps of: supplying a hydrogen-containing inactive gasconsisting of less than 10 volume % of hydrogen gas and the remainingvolume of inactive gas to said methanol reformer and said carbonmonoxide remover thereby to reduce said methanol reforming catalyst andalso to activate said carbon monoxide removing catalyst; and theninitiating methanol reforming reaction and carbon monoxide removalreaction on said reformed gas.